Oblique cutting as a method for determination of the fractural properties of oriented wood tissue

Prikazana je metoda določevanja kritične koncentracije napetosti na podlagi dolžine segmenta odrezka tipa I, nastalega v procesu premočrtnega ortogonalnega odrezavanja bukovine (Fagus silvatica) v smeri 90°-0°. Eksperimentalni rezi so bili narejeni na 10 mm debelih vzorcih pri cepilnem kotu 31° in 42°, debelina odrezka pa se je spreminjala v območju med 0,1 in 0,3 mm. Z metodo končnih elementov smo modelirali reprezentativni segment odrezka različnih dolžin in debelin. Spreminjali smo obremenitev segmenta ter vsakič izračunali koncentracijo napetosti na konici razpoke ter tlačno napetost v hipotetičnem odrezku. Ob predpostavki, da se razpoka pri ločevanju tkiva širi zgolj v primeru, ko je koncentracija napetosti v njenem korenu kritična, ter da se tlačne napetosti v nastajajočem odrezku nenehno povečujejo vse do mejne vrednosti, lahko na osnovi znane dolžine reprezentativnega segmenta odrezka in tlačne trdnosti vzdolž poteka tkiva izračunamo kritično koncentracijo napetosti oziroma določimo lomno togost aktualnega materiala. Razpoka napreduje namreč vse dokler tlačna napetost ne doseže porušne vrednosti, kar se zgodi na mestu loma odrezka. Kritične koncentracije napetosti, ki smo jih določili na osnovi dolžine reprezentativnega segmenta odrezka debeline 0,3 mm, se zelo dobro ujemajo z vrednostmi, dobljenimi s klasičnim frakturnim testom. Pri manjših debelinah odrezka prihaja do manjših odklonov, kar je najverjetneje posledica povečane asimetrije vzorca. Prikazano metodo lahko nedvomno označimo kot učinkovito in verodostojno, kar je tudi najbolj pomembno. Metoda je zelo enostavno in hitra, kajti lomne lastnosti aktualnega materiala je praktično moč določiti že z enim samim premočrtnim rezom. Treba je tudi poudariti, da je priprava vzorčnega materiala nezahtevna, kajti edino, na kar moramo paziti, je usmerjenost tkiva.The method for determination of critical stress intensity factor based on chip segment length of chip type-I originating from orthogonal oblique cutting of beech wood (Fagus silvatica) in the 90°-0° direction is shown. Experimentalcuts on 10 mm thick specimen with rake angles 31° and 42° were made, and the chip thickness varied between 0,1 mm and 0,3 mm. Using the finite element method, we modelled a representative chip segment of varying length and thicknesses. We varied the load at the chip segment and calculated,for each case, stress intensity at the crack tip and compressive stress in hypothetical chip. On presumption that the crack propagates during tissue separation only when the stress intensity at the crack tip equals the critical stress intensity and the compressive stress rises in chip formation process up to the limit strength, we can calculate the critical stress intensity factor by knowing the chip segment length and compressive strength in longitudinal direction. Specifically, the crack propagates until the compressive stress reaches the strength, which occurs at the place of chip break. Critical stress intensity factor calculated from representative 0.3 mm thick chip segment length agrees well with values obtained with classical fracture tests. The results obtained from thinner chip segments deviates to a lesser extent, which is most probably a consequence of highly unsymmetrical specimen. The method has been undoubtedly shown as effective and reliable, which is the most important. The method is very simple and fast, enabling us to determine the fracture properties practically with a single oblique cut. It has to be emphasized, that the specimen preparation is also undemanding, for the only thing we have to pay attention to is the tissue orientation

Cantilever clamping rigidity impact on dynamic modulus of elasticity calculation

Članek prikazuje vpliv vpenjalnega razmerja konzolno vpetega bukovega preizkušanca (Fagus sylvatica) na izračun dinamičnega modula elastičnosti. Najprej smo vzorcu izmerili frekvenco prvega načina lastnega dušenega prečnega nihanja nosilca s prostima koncema. Nato smo skladno z Bernoulli-Eulerjevo teorijo za omenjene pogoje izračunali modul elastičnosti, ki nam je rabil za referenco. Preizkušanec smo zatem konzolno vpenjali od vpenjalnega razmerja 18 do 105 ter mu vsakokrat izmerili frekvenco prvega načina lastnega dušenega prečnega nihanja. Skladno s teorijo za togo konzolno vpetje smo izračunali modul elastičnosti in ga primerjali z referenčnim. Izkazalo se je, da je napaka pri manjših razmerjih vpetja okoli 20 %, pri večjih pa se zmanjša na 5 %. Razlog za veliko napako je nezadostna togost vpetja preizkušanca, ki je kljub zadostni togosti vpenjalnega sistema posledica kompresibilnosti preizkušanca v prečni smeri, saj je modul elastičnosti v radialni oz. tangencialni smeri več kot desetkrat manjši od modula vzporedno s potekom tkiva.The paper presents the impact of the clamping ratio of a clamped beech (Fagus sylvatica) cantilever specimen on the calculation of a dynamic modulus of elasticity. First we measured the specimen\u27s frequency of the first mode of damped transverse free vibrations of a specimen with free ends. In accordance with the Bernoulli-Euler theory, we then calculated the modulus of elasticity for the mentioned conditions, which we subsequently used as a reference. The specimen was then clamped as a cantilever beam several times, from a clamping ratio of 18 to 105, and each time the frequency of the first damped transverse free vibrations was measured. The modulus of elasticity was calculated according to the theory for rigid cantilever clamping, and compared to the reference module. In the case of small clamping ratios, the error was around 20 %, whereas in the case of large clamping ratios the error decreased to 5 %. The cause of the major error is insufficient specimen clamping rigidity, which is due - despite a sufficient rigidity of the clamping system - to the specimen compressibility in the transverse radial or tangential directions where the modulus of elasticity is more than ten times smaller than the modulus along the tissue

Resonance in idling circular saw blades

V članku je prikazana analiza aerodinamičnega vzbujanja prosto vrtečega se krožnega žagnega lista. Ko se krožni žagni list prosto vrti, se zrak v pazdušnem prostoru ozobljenega dela orodja pri prehodu rezila loči od njegovihmejnih bočnih površin in tvori spremenljivo valovito brazdo oziroma turbolentni tok zraka. Posledica časovno spremenljivega turbolentnega toka je nastanek spremenljivega tlaka zraka ob površnah rezila, kar predstavlja aerodinamično vzbujanje žagnega lista. Za pojav prečnega resonančnega nihanja orodja ne zadošča zgolj aerodinamično generirana vzbujevalna sila s primerno frekvenco. Poleg omenjenega pogoja morata biti namreč izpolnjena še dodatna pogoja, in sicer morajo biti vzbujevalne tlačne razlike okoliškega zraka primerno velike, dušilne sposobnosti materiala nosilnega telesa žagnega lista pa dovolj majhne. Ugotovili smo, da nikoli nista vzbujena dva ali več lastnih načinov nihanja hkrati in da je prehod iz enega resonančnega stanja v drugega skokovit. Z naraščajočo frekvenco vrtenja se praviloma povečuje tudi območje vrtljajev, v katerem pride do aerodinamične vzbuditve lastnih nihajnih načinov.The article deals with the analysis of the aerodynamic excitation of a freely rotating circular saw blade. When the circular saw blade rotates freely, the air in the gullet spaces of the rim area of the tool separates (in the passing of the knife from its border flanking surfaces) and forms a variable waveform wake or turbulent airflow. The consequence of the time-variable turbulent airflow is the occurrence of variable air pressure along the knife surfaces, which constitutes the aerodynamic excitation of the saw blade. For the occurrence of transversal resonant vibration of the tool, there does not suffice only aerodynamically generated excitation force at a suitable frequency. In addition to the said condition, two additional conditions must also be met: the exciting pressure differences of the surrounding air must be adequately large, and the damping capabilities of the material of the saw plate sufficiently small. We have found that two or more natural manners of vibration are never excited simultaneously and that the transition from one resonant condition into another is abrupt. With the increasing frequency of rotation there is also, as a rule, an increase in the range of rotations in which the aerodynamic excitation of natural manners of vibration occurs

Influence of Tool Wear on the Quality of the Newly Formed Surface in the Drilling of Wood Composites

The geometry of a drilling tool largely affects the quality of the newly formed surface. When drilling through a composite panel, the hole edge quality on the outlet side is significantly worse than on the inlet side, so the choice of the appropriate tool geometry is crucial. Even if the tool geometry is correct, tool wear also has a strong influence on the quality of the newly formed surface of the holes. With the tool wear, the force in the direction of drilling and torque around the axis of drilling are increasing which can affect to the delamination of particle board on the outlet side. The proposed model for hole edge quality prediction on the outlet side was tested on an experimental model where the cutting forces and torque in the drilling direction were measured, and the quality of the newly formed surfaces was evaluated every 180 holes using a visual method

Moving Home: The Art and Embodiment of Transience Among Youth Emerging from Canadas Child Welfare System

Youth who have exited the child welfare system are among the most vulnerable in Canada. Ample research in social sciences disciplines outside of Geography have illustrated the significant likelihood of poorer life outcomes for former youth in care across a variety of indicators. Combining geographies of mobilities, childrens geographies, and emotional geographies, this research seeks to understand the embodied experiences of former youth in care as they relate the transience experienced in care in the past and lived on in the present. Using arts-based, participatory and Indigenous methods this comparative study collaborated with 15 co-researchers from Toronto and Whitehorse ages 18-30 with lived-experience in care. Representations of bodies were complex, partial, and most often created by female-identified co-researchers. An interesting finding was positive representation of and identification with nature and natural elements, while homes and depictions of them hardly present in comparison. Hope for the future and other youth in care emerged as strong theme, and this hope connects to resilience as practiced by co-researchers as a conscious form of resistance. Methodological findings include the compelling nature of the data created by opening up artistic medium to be self-selected. Lastly, policy suggestions for housing and transition supports to be more understanding of the mobility of these young people are discussed

Single Human Cells Use Transcriptional Mechanisms to Compensate for Differences in Cell Size and DNA Content

Human cells are dynamic: they grow, replicate their genetic information (DNA), and divide. Clonal populations of cells can display marked heterogeneity in size, leading to significant variability in the ratio of DNA to cellular volume. Despite this variability, cells must maintain a constant concentration of RNA and protein, produced from DNA, to ensure proper functionality. How do larger cells produce more output from the same amount of DNA? How do cells that have replicated their DNA prior to cellular division produce the same output as before? Using RNA fluorescence in situ hybridization (RNA FISH), we visualize and count individual RNA molecules in single cells, allowing for precise quantification of transcriptional output of single genes. We also use single-cell RNA sequencing to quantify transcriptional output from all ~20,000 genes encoded in the genome simultaneously. Surprisingly, we discovered that the cell implements two separate transcriptional mechanisms to compensate for changes in cell size and DNA content. Through cell-fusion experiments, we show that a diffusible trans factor, which we believe may be RNA polymerase II, increases transcriptional burst size in larger cells, compensating for changes in volume. Meanwhile, a DNA-linked cis-acting factor reduces the frequency of transcription per gene copy by a factor of two upon DNA replication, allowing the cell to still produce the same amount of RNA after replication, despite having twice the number of DNA copies. We show that transcription depends strongly on volume, and we therefore present a new noise measure which provides a measure of gene expression variability that takes volume into account. We perform single-cell RNA sequencing to measure noise genome-wide, and find that cell-type-specific genes tend to exhibit more expression noise than genes that are ubiquitously expressed across cell types. Finally, we have uncovered a fundamental mechanism by which cells are able to functionally compensate for naturally-occurring variability in size and DNA copy number

Utjecaj modifikacije drva na prijenosnu funkciju mosta za violinu

The violin bridge is an important component of a violin since it transmits the excitation forces from the string to the violin body. Depending on its structure, at a certain frequency spectrum, the bridge acts as a damper or amplifier of excitation forces, which depends on its transfer function. In the study, transfer functions in the range from 400 Hz to 7000 Hz in vertical directions of 3 bridges were measured. The bridges were made from maple wood and supplied by different manufacturers. The bridges were then thermally modified, and the transfer functions were measured again. To determine the influence of thermal modification on material properties, a sample of maple wood was also modified together with the bridges, and the modulus of elasticity and shear modulus before and after the modification were measured. Using Ansys software, a bridge was modelled by the finite element method, by which natural frequencies and transfer functions before and after the modification were calculated. It can be confirmed from the research that wood modification influences the bridge transfer function and that the finite element method can be used to determine the dynamic properties of the bridge by knowing the wood material properties and, therefore, to predetermine the transfer function of the violin bridge before its production.Most na violini važan je dio toga glazbala jer prenosi pobudne sile iz žica u tijelo violine. Ovisno o svojoj strukturi, most na određenome frekvencijskom spektru djeluje kao prigušivač ili kao pojačalo pobudnih sila, što ovisi o njegovoj prijenosnoj funkciji. U istraživanju su mjerene prijenosne funkcije u rasponu od 400 do 7000 Hz u okomitim smjerovima na tri mosta. Mostove od javorova drva izradili su različitih proizvođači. Naknadno su mostovi toplinski modificirani i ponovo su izmjerene njihove funkcije prijenosa. Da bi se utvrdio utjecaj toplinske modifikacije na svojstva materijala, zajedno s mostovima modificiran je i uzorak javorova drva te su izmjereni modul elastičnosti i modul smicanja prije i nakon modifikacije. Uz upotrebu softvera Ansys most je modeliran metodom konačnih elemenata, kojom su izračunane prirodne frekvencije i funkcije prijenosa prije i nakon modifikacije. Na temelju istraživanja može se potvrditi da modifikacija drva utječe na funkciju prijenosa mosta i da se metodom konačnih elemenata mogu odrediti dinamička svojstva mosta ako su poznata svojstva drvnog materijala. Prema tome, prijenosna funkcija mosta violine može se odrediti unaprijed, prije njegove izrade

Structure of DNA-Functionalized Dendrimer Nanoparticles

Atomistic molecular dynamics simulations have been carried out to reveal the characteristic features of ethylenediamine (EDA) cored protonated poly amido amine (PAMAM) dendrimers of generation 3 (G3) and 4 (G4) that are functionalized with single stranded DNAs (ssDNAs). The four ssDNA strands that are attached via alkythiolate [-S (CH2)6-] linker molecule to the free amine groups on the surface of the PAMAM dendrimers observed to undergo a rapid conformational change during the 25 ns long simulation period. From the RMSD values of ssDNAs, we find relative stability in the case of purine rich ssDNA strands than pyrimidine rich ssDNA strands. The degree of wrapping of ssDNA strands on the dendrimer molecule was found to be influenced by the charge ratio of DNA and the dendrimer. As G4 dendrimer contains relatively more positive charge than G3 dendrimer, we observe extensive wrapping of ssDNAs on the G4 dendrimer. The ssDNA strands along with the linkers are seen to penetrate the surface of the dendrimer molecule and approach closer to the center of the dendrimer indicating the soft sphere nature of the dendrimer molecule. The effective radius of DNA-functionalized dendrimer nanoparticle was found to be independent of base composition of ssDNAs and was observed to be around 19.5 {\AA} and 22.4 {\AA} when we used G3 and G4 PAMAM dendrimer as the core of the nanoparticle respectively. The observed effective radius of DNA-functionalized dendrimer molecule apparently indicates the significant shrinkage in the structure that has taken place in dendrimer, linker and DNA strands. As a whole our results describe the characteristic features of DNA-functionalized dendrimer nanoparticle and can be used as strong inputs to design effectively the DNA-dendrimer nanoparticle self-assembly for their active biological applications.Comment: 13 pages, 10 figures, 3 Table

Simultaneous enumeration of cancer and immune cell types from bulk tumor gene expression data.

Immune cells infiltrating tumors can have important impact on tumor progression and response to therapy. We present an efficient algorithm to simultaneously estimate the fraction of cancer and immune cell types from bulk tumor gene expression data. Our method integrates novel gene expression profiles from each major non-malignant cell type found in tumors, renormalization based on cell-type-specific mRNA content, and the ability to consider uncharacterized and possibly highly variable cell types. Feasibility is demonstrated by validation with flow cytometry, immunohistochemistry and single-cell RNA-Seq analyses of human melanoma and colorectal tumor specimens. Altogether, our work not only improves accuracy but also broadens the scope of absolute cell fraction predictions from tumor gene expression data, and provides a unique novel experimental benchmark for immunogenomics analyses in cancer research (http://epic.gfellerlab.org)